Charles Murray has acquired some bitter enemies. In 1984 he attracted strident criticism for arguing that the "war on poverty" was increasing the number of poor people. The criticism turned to plain hostility in 1989 when he popularised the term "underclass" and then morphed into sheer hatred in 1994 when The Bell Curve discussed the average IQs of different ethnic groups. And yet Murray is a mild-mannered scholar with a penchant for number-crunching who writes and speaks in the folksy style of America's Midwest.

He first came to international attention with his book, Losing Ground, which argued that massive welfare spending was making matters worse. In 1968 13 per cent of Americans were below the official poverty line. By the time Reagan was elected in 1980 expenditure had increased fourfold, but poverty was still put at 13 per cent. Welfare policies loomed large for low-income Americans, and encouraged behaviour that chipped away at personal independence, by weakening incentives to work hard and raise children within marriage.

In Pursuit: Of HappinessandGood Government followed in 1989. It was a passionate defence of the guiding hopes of the American founders. Among the "unalienable rights" to be secured by American governments was the "pursuit of happiness". But what had the founders understood by "happiness"? Certainly they had not meant self-absorption in personal pleasures, but rather a society in which people lived as "wisely and fully as they could". And the job of government was to enable them to do so.

Enthusiasts for freedom often divide into two groups — libertarians and classical liberals. Libertarians tend to see freedom as the power available to each individual compared with everyone else. Kant called it "wild freedom" and compared it with "civil freedom", which he thought was the only kind that could be enjoyed by everyone living together in the same land. Strangely Murray has always called himself a libertarian, but the paradox is explained in What it Means to Be a Libertarian (1997), where he calls himself a "lower-case libertarian", too fond of the "indispensable role of tradition and the classical virtues" to go along with the followers of Ayn Rand. He was firmly in the tradition of Adam Smith and "conservative hero" Edmund Burke.

Murray does not make the mistake of those economists who think that a free society must always maximise economic efficiency. Murray wants freedom of economic action but regards economic efficiency as a "pleasant bonus". Even if a market economy were less efficient than collectivism at producing wealth, it would still be morally superior and therefore preferable.

The Bell Curve, co-authored with Richard Herrnstein, came out in 1994 and was the book that got Murray into most trouble.It noted that the highest average IQ scores are achieved by Asian-Americans, followed by European-Americans, and then by African-Americans. In Losing Ground Murray had said that race was "not a morally admissible reason for treating one person differently from another. Period." But many critics of The Bell Curve didn't believe him and attacked the book as racist.

Defenders of Murray argued that he had met such violent hostility because he destroyed the faith of egalitarians that government action could manipulate human affairs for the better. For them, society was the cause of problems, not personal attributes. Murray accepted that there were "huge and often intractable individual differences that shape human society", but his view was a counsel of realism, not despair. The Bell Curve celebrated "the capacity of people everywhere...to live morally autonomous, satisfying lives".

In 1989 the Sunday Times asked Murray to investigate whether we had an "underclass". In 1999 they brought him back to review progress, with Underclass +10. In 1989 he had used three measures: drop-out from the labour force among young males, violent crime, and births to unmarried women. He thought they were associated with the growth of a class of "violent, unsocialised people who, if they become sufficiently numerous, will fundamentally degrade the life of society". In 1999 formerly law-abiding Britain had become "just another high-crime industrialised country". The underclass was "driven by the breakdown in socialisation of the young, which in turn is driven by the breakdown of the family", but the government was not even willing to state that the family was important.

He is least known for his most outstanding book, Human Accomplishment, where he described the main human achievements from 800BC to 1950 in music, literature, the visual arts, medicine and the physical sciences, explaining why Western culture had been more successful than others.

Murray will be remembered as one of the great champions of liberty. His new book, Coming Apart: The State of White America 1960-2010, develops his argument that class divisions have weakened American civic culture. A new elite cut off from middle-class America is emerging, while a growing lower class rejects mainstream commitments to work, religious faith, marriage and respect for the law.